1. Field of the Invention
A device and method for elongating a bone, and, more particularly, a modular distractor comprising a extendable member having an adjustable length and absorbable footplates releasably affixed to opposing ends thereof.
2. Prior Art
The general idea of using distraction osteogenesis to elongate bone was reported as early as 1954. Although the technique offered important advantages over prior art methods of bone elongation such as autogenous bone grafting, the technique received relatively little attention in the literature until recently. Ilizarov et al., in U.S. Pat. No. 4,615,338, discloses an apparatus for bone compression or elongation. Muschler, et al., in U.S. Pat. No. 5,429,638, disclose a intermedullary inplant useful for elongating a bone. Other patents disclosing extendable, implantable distraction devices include U.S. Pat. Nos. 5,129,903, 5,364,396, 5,976,142, 5,902,304, 5,873,715 and 5,810,812.
When a bone is broken to enable the controlled mechanical separation of juxtaposed ends of the broken bone, the growth of new bone therebetween (osteogenesis) occurs and may be used to elongate and/or reshape the bone. A distraction osteogenesis device has at least two footplates having screw holes therein and an extendable member therebetween providing means for changing the distance between the footplates. In the performance of the distraction osteogenesis procedure, at least two footplates are affixed to the bone on either side of a fracture by means of screws. The footplates are connected to one another by the extendable member, at least a portion of which spans the fracture site and provides means for stabilizing the osteotomized bony fragments. The footplates and extendable member are collectively referred to as a distractor.
Following implantation of the distractor, the extendable member is periodically manipulated to incrementally separate the bones affixed to the respective footplates. Osteogenesis is sustained within the fracture site as the juxtaposed ends of the bone incrementally separate. When the bone attains a desired length and/or curvature, further elongation of the distractor is discontinued and the newly formed bone is permitted to harden. The distractor is then surgically explanted by unscrewing the footplates from the bone.
The process of distraction osteogenesis begins when a distraction force is applied to a healing callus which joins divided bone segments, and continues for as long as the bone is stretched. The distraction force applied to the bone also creates tension in the surrounding soft tissue. The tension on the bone-associated soft tissue initiates a sequence of adaptive changes, collectively referred to as distraction histogenesis. Thus, skin, fascia, muscle, blood vessels, nerves and tendons undergo distraction histogenesis concurrently with osteogenesis and the adaptive changes in these tissues help to support the bone during and after distraction osteogenesis. It is, therefor, important avoid disturbing such soft tissue when the procedure is completed.
A common feature of prior art distractor devices employed for osteogenic bone elongation include means for rigidly attaching opposing ends of an extendable member to a surgically severed bone (i.e. a bone having an osteotomy) such that the extendable member straddles the osteotomy. The means for attaching the distractor to the bone, or "footplates", comprise plates generally resembling bone plates, having screw holes therein and means thereon for attaching an extendable member thereto. Such footplates are fabricated from a biocompatible metal such as titanium, stainless steel or cobalt chrome alloy. Upon completion of distraction osteogenesis, the footplates must be surgically removed. The trauma of an additional surgical procedure for the explantation of the distractor includes possible damage to adjacent vital structures, swelling, risk of infection and the need (usually) to subject the patient to a general anesthesia. Thus, there remains a need for an osteogenesis distractor device which eliminates the need for a second surgical procedure to explant the distractor footplates.